Digging into the details of Orion’s EM-1 test flight

As NASA continues to analyze and refine the profile for the Exploration Mission-1 (EM-1) test flight, more information about the multi-week mission is beginning to be detailed. The Orion spacecraft will fly into orbit around the Moon before returning to Earth in a shakedown mission before the first crew flies in Orion on Exploration Mission-2 (EM-2).
EM-1 will be the first flight of Orion’s European Service Module, also pairing it with the Crew Module for the first time, with hundreds of test objectives to be evaluated during the mission.

Orion will fly on EM-1 for the first time with all of its primary spacecraft elements. The European Service Module (ESM) will make its first flight, connected to the second crew module (CM) unit by a crew module adapter (CMA) making its first flight.

The integrated spacecraft will be tested on a multi-week flight to a Distant Retrograde Orbit (DRO) around the Moon and back. “The missions are either 26-27 days or they’re going to be 38 to 42 days and there’s nothing in between,” Nujoud Merancy, Exploration Mission Analysis Lead at NASA’s Johnson Space Center, said in an interview with NASASpaceflight.com. “The difference is the DRO orbit is a twelve-day period, so one lap around the Moon takes twelve days.”

“In a short mission you’re only there for half an orbit so you enter sort of in front of the Moon and you depart from behind it so you’ve only gone halfway around,” she explained. “For the long mission then you stay for another orbit, so you’ll do one and a half times around the Moon with the long class.”

The long class mission duration was added to provide the required lighting conditions for landing and recovery for any time of the year. The ESM will provide the CM with the power and consumables to fly crew for as much as three weeks and without crew for over half a year. “We’re certifying this vehicle for those 40 days but the Orion requirements are 21 crewed days and 210 uncrewed days, so in theory the mission could be 231 days within our requirements base,” Merancy noted.

Without a crew on board, NASA and prime contractor Lockheed Martin will take the opportunity to exercise the other vehicle subsystems for possibly up to six weeks, but the mission duration won’t stress the overall requirements.

“Once you take the people out it’s really a matter of how much prop (propellant) are you using and if all you’re doing is attitude control you really don’t burn prop very quickly or if you were docked to the LOP-G (the proposed Lunar Gateway), then we’re not even using our attitude control system so you could just be there for a long time,” she said.

“So uncrewed there’s not a whole lot of limitations, it’s now valve seals and things like that. The lifetime certification should be over 200 days for the vehicle.”

“That’s why when we switched from the [short duration only mission] to the include the long class on this one it wasn’t really that it was stressing anything,” she added. “People have to go back and make sure their systems are all still good, but it was a pretty easy change to insert for the mission because when it’s uncrewed there’s not much difference in the vehicle operation.”

Merancy noted that Lockheed has done studies in the past looking at how to fly Orion for 1000 days. “There’s only like a few things you change and it’s really like changing out a few seals,” she explained. “If you want a thousand day vehicle then you can’t have even the minor leakage that occurs through the hatch seals, you want like a third seal in there, right?”

“So there’s a few things you change, but a thousand-day Orion isn’t much of a difference from a 200-day Orion.”

Orion test flight

EM-1 is a first flight for most of NASA’s current human exploration programs. The Orion crew module is one of the only major elements not making its debut; its first flight was Exploration Flight Test-1 (EFT-1) in late 2014, where it was launched by a Delta IV Heavy booster with mass simulators for the most of the Service Module elements.

Flying on this flight integrated with a Service Module making its debut, this Orion will be carried into orbit by the Space Launch System (SLS) rocket on its first launch. Orion and SLS will also liftoff on EM-1 in the first launch from Exploration Ground Systems’ rebuilt launch operations infrastructure at the Kennedy Space Center in Florida.

A still from animation of SLS launching Orion on EM-1. Credit: NASA.

NASA and its contractors have been studying and analyzing the EM-1 mission profile for a long time. Early plans were to fly a shorter circumlunar flight test, but it was subsequently decided to use the flight to demonstrate one of the tactical Design Reference Missions (DRM), which is to fly to DRO.

The spacecraft has hundreds of test objectives on EM-1. “We have something like a hundred thirty FTOs, flight test objectives,” Merancy said. “The three big priorities are the lunar velocity heat-shield reentry, the end to end entry sequence, and the in-space demonstration of all the subsystems.”

“The whole flight is to make sure the vehicle works, so pretty much every subsystem has objectives to evaluate after the flight, for how well did it perform. You have really obvious ones like ‘must do main engine burns.’ The nominal mission execution will hit almost every single objective you need, because in order to execute the mission you need to use the main engine and you have to use the power and thermal [systems].”

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SLS will first insert Orion and its Interim Cryogenic Propulsion Stage (ICPS) into Earth orbit, followed by ICPS making a long Trans-Lunar Injection (TLI) burn at the end of the first orbit. Separation from the ICPS will largely mark the end of the SLS test flight and the beginning of Orion’s.

Springs will push Orion away from the ICPS about ten minutes after TLI cutoff. The springs will provide some separation velocity between spacecraft and upper stage, but Orion will also fire its auxiliary engines to increase the separation rate after coasting away from ICPS for over a minute.

Orion has had three types of engines on the ESM: reaction control system (RCS) thrusters for attitude control and small translational maneuvers, auxiliary (Aux) engines for most translational maneuvers, and an Orbital Maneuvering System engine (OMS-E) for large translational burns.

If necessary, there are multiple opportunities for Orion to make outbound trajectory correction (OTC) maneuvers on the way to the Moon; on its first flight, the plan is to use the first opportunity a few hours after TLI to test-fire the OMS-E.

“[For] the first outbound trajectory correction we’re going to do an OMS Check-Out/OCO burn because in all likelihood the burn you need for the correction would be so small you don’t need to use the OMS,” Merancy explained. “It’s likely you’d do it on Aux and it’d just be a little correction for whatever dispersion ICPS drops us off at.”

Orion ESM propulsion system elements, showing the three types of engines: RCS thrusters grouped in pods and Auxiliary engines at the bottom surrounding the main OMS engine. Credit: Airbus DS.

“That means that the first time you ever use the OMS engine would be on the far side of the Moon when you don’t have comm (communications), so that’s kind of dumb,” she said.

Orion will make a pair of burns with its main engine to enter and leave DRO. Entering, the spacecraft will make that Outbound Powered Flyby (OPF) “far side” burn near closest approach to the Moon at an altitude of around 100 km, which sets up a Distant Retrograde orbit Insertion burn (DRI) around four days later. Orion will leave DRO the opposite way, with a Distant Retrograde orbit Departure (DRD) burn first, setting up a Return Powered Flyby (RPF) burn to return to Earth.

The OCO burn gives the flight control team and the program a chance to evaluate engine performance within the spacecraft system early in the mission. The engine itself is a space veteran, flying on several Space Shuttle missions; however, this is the first time it is integrated with a different spacecraft.

Orion and Earthrise from the Moon. Credit: Nathan Koga for NSF/L2.

The trajectory might not need to be corrected, so it’s likely almost all of the velocity components of the OCO burn will be out of plane. “We’re going to intentionally do an OMS burn which means it has to be bigger than you need and you’ll just burn in a sort of a null direction,” she explained.

“If you burn perpendicular to the velocity vector it really doesn’t affect the trajectory, so you’ll just put whatever component you need for correction in and then burn a bunch out of plane so you can get a 30-second OMS burn in and confirm that the engine and all the systems are working right there at the beginning of the flight.”

Merancy noted that the minimum burn time for the OMS engine on Orion is five seconds, but it has to run longer than that for the vehicle guidance system. “We’re just sort of doing a wasting burn if you will, so most of it won’t do anything to the mission, but you have to turn on the engine long enough,” she noted.

“To get a whole guidance cycle where it actually closes the loop and calculates it all, that’s 30 seconds so that’s why we’re doing a 30 second burn there.”

Most of the time on the long coast periods outbound to and returning from the Moon, Orion will be in a tail-to-Sun attitude. “Our vehicle design is the tail-to-Sun flight attitude, so that way your arrays get full Sun and the radiators are around the barrel [are] looking at deep space. So that tail-to-Sun is sort of our baseline power/thermal-balanced attitude.”

“Nominally, the vehicle could just sit there in ‘tail to sun’ indefinitely, but we do have other things that you have to do, like the IMUs (Inertial Measurement Units) will need to be aligned and you’ll need to do star-tracker takes and stuff,” she added. “So there will be times you’ll go out of attitude just to get data and align the IMUs, but you’ll just keep going back to tail to sun.”

“You don’t have to hold it that tight. So when you’re sitting tail-to-Sun you can just bounce around in there, because it just drives up your prop quantity [consumption] to hold it really tight and you don’t need to. The arrays can track plenty and you’ve 40 degrees worth of ‘slosh,’ so GNC doesn’t need a tight deadband on that.”

Crew module outfitting

The EM-1 Orion crew module won’t have much in the way of crew systems on this flight, but it will be outfitted with some hardware.

“For this flight I think we have at least one or two seats installed because there is going to be a dummy put in with a radiation vest and stuff like that, so at least some of it will be accurate, but we aren’t putting in the crew displays and we don’t have the ECLSS (Environmental Control and Life Support System) wall installed, which is at sort of the back of the cabin,” Merancy explained.

Presentation figure showing basic layout of fully outfitted crew module. For EM-1, the top two seats are planned to be installed, but most of the crew equipment shown here will make its first flight on EM-2. Credit: NASA

“That’s not going in this flight. I think the floor panels will be in, and at least two seats I think and a dummy, so there will be some stuff in there, but it still won’t look like the true EM-2 crew vehicle. There will be cameras hard mounted and things like that which wouldn’t be there for EM-2, though.”

There will be opportunities to downlink imagery from spacecraft cameras during the flight, but they will be more limited than Earth-orbiting spacecraft. “I think we get live video, some of it will be fairly low quality,” she said. “I think we get sequential still video and we can downlink high-res pictures.”

Merancy noted that she’s looking forward to pictures taken from outside: “We have cameras on the tips of all the solar arrays, so that means we can take a selfie with the Moon, so that’s going to be the one that I’m waiting for.”

Although live imagery feeds may be limited, a lot of video will be recorded on the vehicle. “There’s a bunch of data recorders on board, so a lot of it is recorded on board and will be pulled off when we land,” she said.

Orion takes a selfie from DRO. Credit: Nathan Koga for NSF/L2.

In addition to providing long-term power for CM systems, the ESM design carries crew-related consumables such as cabin atmosphere, but only one of those will be connected to the CM through the CMA on EM-1. “The nitrogen tank — I think that’s the only one that’s hooked up all the way to the CM,” Merancy said.

“There is a nitrogen tank because you will use that if there is a leak to repressurize because the cabin needs the pressure for reentry. They are flying the water tanks, but they’re not plumbed to the CM.”

For launch, the cabin will start with fresh air from the launch site. “It’ll be Florida air when the hatch gets closed,” she said. “I think we have sensors on-board so we can…measure if there’s any cabin leaks in flight and the humidity level and stuff like that, but the humidity level shouldn’t change.”

Orion’s hatch won’t be closed for flight until shortly before or during the launch countdown in order to allow for late configuration of items in the cabin and late stow of experiments. Although there is no crew, the Crew Access Arm on the Mobile Launcher is installed and will be used during the EM-1 launch campaign. “There’s a bunch of late stow items,” Merancy said.

“There’s radiation sensors that are going in…and all that has to be turned on at the last minute. They’re just stowed in there, so there’s no command capability to them. So there is a bunch of late stow [and] a couple of science experiments going in, so at a minimum you need the Crew Access Arm to get to it for those on the pad.”

Most of the ECLSS units won’t fly on Orion until EM-2, but NASA is carrying out ground and flight tests of the other critical systems in preparation for the first crewed flight. “Station has our ECLSS swing bed thing, the whole amine swing bed,” Merancy noted.

“They’ve been doing a demo on orbit for a while now. And they built somewhere around here there’s a test lab where they built up an ECLSS system to start testing it on the ground, so there’s a bunch of mitigations that are being done for the fact that we’re not flying it on EM-1.”

“But the other part of it is that without having a biological person inside the vehicle to use the systems, putting it on there wouldn’t actually test them,” she explained. “So unless you had something like released a CO2 tank you would never know if the swing beds worked even if we had put them on EM-1.”